The present invention relates to a sheet dispenser mechanism. In particular, the invention relates to a sheet dispenser mechanism for use in a self-service terminal (SST) such as an automated teller machine (ATM).
Conventional sheet dispenser mechanisms include a multiple sheet detector for monitoring each sheet being dispensed by the mechanism to ensure that the sheet being dispensed is not in fact two or more sheets stuck together.
Typically, an optical arrangement is used to detect multiple sheets being conveyed as a single sheet. These optical arrangements have the disadvantage that the transmissive qualities of a sheet may vary depending on the sheet design. Another disadvantage is that optical arrangements require sensors to be located within the dispenser mechanism, which occupies space.
It is an object of the invention to obviate or mitigate one or more of the above disadvantages.
According to a first aspect of the invention there is provided a sheet dispenser mechanism characterized by: upper and lower transport guides for conveying a sheet therebetween, only one of the transport guides being movable in a plane transverse to the surface of the sheet; a piezoelectric sensor mechanically coupled to the movable transport guide for detecting movement in a direction transverse to the surface of the sheet; and a detecting circuit for monitoring the output from the piezoelectric sensor.
By virtue of the invention, when a single sheet is being transported the movable transport guide is deflected by the thickness of the sheet and the detecting circuit detects a first voltage associated with that deflection; however, if two or more sheets are stuck together and transported as a single sheet then the movable transport guide is deflected by the thickness of those two or more sheets and the detecting circuit detects a second voltage (larger than the first voltage) associated with the greater deflection, thereby indicating that multiple sheets are present.
Preferably, each of the upper and lower transport guides comprises a shaft having rollers mounted thereon. Alternatively, each of the upper and lower transport guides comprises a shaft having stretchable belts mounted thereon.
Preferably, on detecting multiple sheets the detecting circuit changes the transport path for the multiple sheets so that the sheets are retained in the sheet dispenser mechanism and not dispensed.
Preferably, the piezoelectric sensor comprises a piezoelectric polymer film disposed on a resilient base. Conveniently, the resilient base is made of rubber.
In one embodiment, the sheet dispenser mechanism is incorporated within an SST such as an ATM. When the sheet dispenser mechanism is incorporated in an ATM the sheets dispensed may be bank notes.